In the related art, brass (Cu—Zn alloy) having Cu and Zn as main components has been used for constituent materials for connectors, terminals, relays, springs, sockets, switches, and the like which are used in decoration members such as handrails, door handles, lighting equipment, elevator panels, and the like, construction members, metal fittings and metal goods, or electronic and electrical components, automobile components, communication apparatuses, electronic and electrical apparatuses, and the like. However, under high temperature and high humidity conditions, the color of the brass is changed due to surface oxidation for a short period of time even in a room. As a result, the brass-yellow color is impaired, which causes a problem in appearance. When a transparent clear coating or Ni or Sn plating is carried out to avoid a color change, the antimicrobial performance and the conductivity of the copper alloy are not exhibited in some cases.
In recent years, along with a reduction in size and weight and high performance of apparatuses, connectors, terminals and the like have been required to have extremely strict characteristic improvements and cost performance. For example, a thin sheet is used for a spring contact portion of a connector. However, it is required for a high strength copper alloy which constitutes the thin sheet to have high strength, a high degree of balance between elongation and strength, and resistance to severe use environments, that is, excellent color fastness, stress corrosion cracking resistance, and stress relaxation characteristics so as to realize a small thickness. Further, it has been required to obtain high productivity, particularly, to obtain excellent economical efficiency by keeping the amount of copper used which is a noble metal to a minimum.
Examples of the above-described use environment of the copper alloy include an indoor environment (including the inside of a car) at a high temperature or a high humidity, an environment in which a large number of unspecified people touch the alloy, and an environment including a small amount of a nitrogen compound such as ammonia and amine, and the like. The copper alloy is required to have color fastness and stress corrosion cracking resistance to endure these environments.
In handrails, door handles, unplated connectors, terminals and door handles, and the like, there arise not only problems in appearance and stress corrosion cracking, but also problems of deterioration in antimicrobial properties and conductivity due to oxidation of the surface of brass.
Further, connectors, terminals and the like are used in a cabin of an automobile and a portion close to an engine room under the blazing sun and in this case, the temperature in the use environment reaches about 100° C. High material strength is required in the case in which the thickness of the material has to be reduced. When a copper alloy is used for terminals and connectors, high material strength is required to obtain high contact pressure. However, in the applications for springs, terminals and connectors, the high material strength can be used within a range of stress of the elastic limit at room temperature. However, as the temperature rises in the use environment, for example, when the temperature rises to 90° C. to 150° C. as described above, a copper alloy is permanently deformed. Particularly, in the case of brass, a degree of permanent deformation is great and a predetermined contact pressure cannot be obtained. In order to utilize high strength, a small degree of permanent deformation at a high temperature is demanded and it is preferable that the properties called stress relaxation characteristics are excellent as the measure of the degree of permanent deformation at a high temperature.
However, the plating layer on the surface of a plated product is peeled off by long term use. In addition, when a large amount of products such as connectors or terminals are produced at low costs, in a process of producing a sheet which becomes a material thereof, the surface of the sheet is plated with Sn, Ni and the like in advance and the sheet material is punched and used. In this case, the punched surface is not plated with Sn, Ni and the like and thus color change or stress corrosion cracking easily occurs. Further, when Sn, Ni and the like are included in the plating according to the kind of the plating, it is difficult to recycle the copper alloy.
Here, examples of a high strength copper alloy include phosphor bronze (Cu-6 mass % to 8 mass % Sn—P), and nickel silver (Cu—Zn-10 mass % to 18 mass % Ni). As a general copper alloy which has excellent cost performance and high conductivity and high strength, generally, brass is well-known.
In Patent Document 1, as an alloy which satisfies the requirements for high strength, a Cu—Zn—Sn alloy is disclosed.
On the other hand, constituent members such as side rails, headboards, footboards, handrails, door handles, door knobs, door levers, and medical appliances used in medical institutions, public facilities, facilities and equipment corresponding to these medical institutions and public facilities, and research facilities for strict hygiene management (for example, food, cosmetics, pharmaceutical products and the like), and water supply and drain sanitary facilities and apparatuses such as a drainage tank used in vehicles and the like are formed by joining pipes, sheets, strips, rods, castings, and members formed to have various shapes by forging.
Here, in the case of welding a copper alloy including Zn, since Zn easily evaporates during the welding, a technique is required for welding. In addition, the welding leaves a bead trace in appearance and in order to solve a problem in appearance, a process of polishing a bead trace is added. Depending on the shape, it may be difficult to remove the bead trace completely. Then, there arises a problem in appearance and it takes much time to remove the bead trace. Thus, this case is not preferable. Further, there is a concern of antimicrobial properties (bactericidal properties) being deteriorated.
In order to obtain sufficient antimicrobial properties (bactericidal properties), instead of joining copper alloy members, a method of attaching a thin copper foil or a composite material obtained by bonding a copper foil and a resin or paper to constituent members such as handrails, door handles, door knobs, and door levers has been attempted (for example, refer to Patent Document 2).